Gas turbine load/unload path control

ABSTRACT

A loading/unloading method for a gas turbine system is disclosed. The gas turbine system includes a combustion section featuring a primary combustion stage with a first plurality of fuel nozzles and a downstream, secondary combustion stage with a second plurality of fuel nozzles. For loading, the method progresses through each of a plurality of progressive combustion modes that sequentially activate a higher number of at least one of the first or second plurality of fuel nozzles; and for unloading, the method progresses through each of a plurality of progressive combustion modes that sequentially activate a lower number of at least one of the first or second plurality of fuel nozzles. During each combustion mode, regardless of whether loading or unloading, a primary combustion stage exit temperature of a combustion gas flow is controlled to be within a predefined target range corresponding to the respective combustion mode.

This application is a Divisional application of U.S. patent applicationSer. No. 16/254,909, filed on Jan. 23, 2019, now U.S. Pat. No.11,384,940, the entire contents of which are fully incorporated here.

BACKGROUND OF THE INVENTION

The disclosure relates generally to gas turbine systems, and moreparticularly, to a load/unload path control process for a gas turbinesystem with a two stage combustion section.

Gas turbine systems are used in a wide variety of applications togenerate power. In operation of a gas turbine system (“GT system”), airflows through a compressor and the compressed air is supplied to acombustion section. Specifically, the compressed air is supplied to anumber of combustors each having a number of fuel nozzles, i.e.,burners, which use the air in a combustion process with a fuel. Thecompressor includes a number of inlet guide vanes (IGVs), the angle ofwhich can be controlled to control an air flow to the combustionsection, and thus a combustion temperature. The combustion section is inflow communication with a turbine section in which the combustion gasstream's kinetic and thermal energy is converted to mechanicalrotational energy. The turbine section includes a turbine that rotatablycouples to and drives a rotor. The compressor may also rotatably coupleto the rotor. The rotor may drive a load, like an electric generator.

The combustion section includes a number of combustors that can be usedto control the load of the GT system, e.g., a plurality ofcircumferentially spaced combustor ‘cans.’ Advancements have led to theuse of combustors having two combustion stages. A header (or head end)combustion stage may be positioned at an upstream end of the combustionregion of each combustor. The header combustion stage includes a numberof fuel nozzles that act to introduce fuel for combustion. Advanced gasturbine systems also include a second combustion stage, referred to asan axial fuel staging (AFS) or late lean injection (LLI) combustionstage, downstream from the header combustion stage in the combustionregion of each combustor. The AFS combustion stage includes a number offuel nozzles or injectors that introduce fuel diverted (split) from theheader combustion stage for combustion in the AFS combustion stage. TheAFS combustion stage provides increased efficiency and assists inemissions compliance for the GT system by ensuring a higher efficacy ofcombustion that reduces harmful emissions in an exhaust of the GTsystem. Each fuel nozzle in the header combustion stage can becontrolled to be on or off to control flow of fuel for combustion.Conventionally, a combustion section reference temperature is used tocontrol the combustion section. The combustion section referencetemperature is an estimation of the temperature of the combustion flowat the exit of the combustion region prior to entering the turbinesection.

Loading or unloading a GT system presents a number of challengesrelative to controlling emissions as the GT system gradually increasesor decreases its power output. For example, a start up may begin withthe rotor being rotated by a motor until a speed is reached allowing thecompressor to begin flowing air to the combustion section (i.e., purgespeed). The speed may then be reduced at which point fuel flow isinitiated to the combustion section, and fuel combustion begins. At thispoint, the GT system goes through a number of ‘combustion modes’ inwhich a number of fuel nozzles of the header combustion stage becomeoperative, and then eventually all fuel nozzles in the header combustionstage and the AFS combustion stage become operative. During thisprocess, air flow intake is set by controlling an angle of a stage(s) ofIGVs on the compressor that control air flow volume.

During the progression through the combustion modes, it is verydifficult to control emissions at certain times. To illustrate, FIG. 1shows an illustrative, conventional start up load path graph plottingexhaust temperature (Tx) versus load between full speed no load (FSNL)(0% load) to 50% of rated operation, with a schematic rendition of acarbon monoxide (CO) amount in the GT exhaust in a quasi-steady statewith the load path. Changes in combustion modes are shown with verticalmarks on the load path line. Initially, IGVs are set to a desired angleand an initial exhaust temperature is achieved at FSNL (0% load). Asstartup progresses from 0% to 10% load through three illustrativecombustion modes (vertical marks on load path), exhaust temperaturerises as more fuel nozzles are activated and net fuel flow increaseswhile the air flow remains constant. Exhaust temperature rises until itreaches a plateau at an isotherm exhaust temperature limit for the GTsystem. As shown by the CO emissions schematic rendition, as loadingprogresses through the combustion modes, CO amounts rise and fallthrough the different modes until the final combustion mode in thesequence is employed, i.e., with all fuel nozzles in header and AFScombustion stages activated. Each combustion mode typically includes atleast one period during which the emissions are higher than desired atlow loads. Once the final combustion mode in the sequence has beenengaged, the CO emissions will eventually decrease to compliant levelsas the unit loads. The lowest load at which emissions compliance issatisfied is referred to as the minimum emissions compliance load (MECL)and reflects the turndown capability of the GT system. Conventional loadpath control typically utilizes various control strategies for stage(s)of IGVs, inlet bleed heating, or compressor extraction flow modulationto extend a GT system's low load capability, e.g., during turndown.Using such a strategy may result in low load capability of 30%-45% ofrated power depending on ambient conditions and the technology employedin the GT system.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a loading/unloading method fora gas turbine system, the gas turbine system including a compressorfeeding air to a combustion section that is coupled to a turbine, thecombustion system including a plurality of combustors, each combustorincluding a primary combustion stage including a first plurality of fuelnozzles and a secondary combustion stage downstream from the primarycombustion stage, the secondary combustion stage including a secondplurality of fuel nozzles, the method comprising during loading orunloading: progressing through each of a plurality of progressivecombustion modes that sequentially activate a different number of atleast one of the first or second plurality of fuel nozzles; and duringeach combustion mode regardless of whether loading or unloading,controlling a primary combustion stage exit temperature of a combustiongas flow to be within a predefined target range corresponding to therespective combustion mode.

A second aspect of the disclosure provides a gas turbine (GT) system,comprising: a compressor; a combustion section including a plurality ofcombustors, each combustor including a primary combustion stageincluding a first plurality of fuel nozzles and a secondary combustionstage downstream from the primary combustion stage, the secondarycombustion stage including a second plurality of fuel nozzles; a turbinesection downstream of the combustion section; a control system coupledto the combustion section and configured to, during a loading orunloading of the GT system: progress through each of a plurality ofprogressive combustion modes that sequentially activate a differentnumber of at least one of the first or second plurality of fuel nozzles;and during each combustion mode regardless of whether loading orunloading, control a primary combustion stage exit temperature of acombustion gas flow to be within a predefined target range correspondingto the respective combustion mode.

A third aspect of the disclosure provides a non-transitory computerreadable storage medium including code for a control system of a gasturbine system, the code configured to control a combustion sectionincluding a plurality of combustors for a gas turbine system, eachcombustor including a primary combustion stage including a firstplurality of fuel nozzles and a secondary combustion stage downstreamfrom the primary combustion stage, the secondary combustion stageincluding a second plurality of fuel nozzles, the code performing thefollowing during loading or unloading: progressing through each of aplurality of progressive combustion modes that sequentially activate adifferent number of at least one of the first or second plurality offuel nozzles; and during each combustion mode regardless of whetherloading or unloading, controlling a primary combustion stage exittemperature of a combustion gas flow to be within a predefined targetrange corresponding to the respective combustion mode.

The illustrative aspects of the present disclosure are designed to solvethe problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the disclosure taken in conjunction with the accompanyingdrawings that depict various embodiments of the disclosure, in which:

FIG. 1 shows an illustrative conventional start up load path graphplotting exhaust temperature (Tx) versus load from FSNL (0% load) up to50%, and with a schematic rendition of a carbon monoxide (CO) emissionsin the GT exhaust in a quasi-steady state adjacent the load path.

FIG. 2 shows a partial cross-sectional side view of a gas turbine systemaccording to an embodiment of the disclosure.

FIG. 3 shows a cross-sectional side view of a combustor for a combustionsection useable in GT system of FIG. 2.

FIG. 4 shows a plan view of a cap assembly of the combustor of FIG. 3,as viewed from the aft end of the combustor looking upstream, accordingto a first aspect herein.

FIG. 5 shows a plan view of an alternate cap assembly of the combustorof FIG. 3, as viewed from the aft end of the combustor looking upstream,according to a second aspect herein.

FIG. 6 shows an illustrative environment including a GT controller and aload/unload control system, according to various embodiments of theinvention.

FIG. 7 shows a flow diagram of an illustrative loading method accordingto embodiments of the disclosure.

FIG. 8 shows an emission compliant start up load path graph plottingexhaust temperature (Tx) versus load from FSNL (0% load) up to 50%, andwith a schematic rendition of a carbon monoxide (CO) emissions in the GTexhaust in a quasi-steady state with the load path, according toembodiments of the disclosure.

FIG. 9 shows a mission compliant unload path graph plotting exhausttemperature (Tx) versus load from 50% down to FSNL (0% load), and with aschematic rendition of a carbon monoxide (CO) emissions in the GTexhaust in a quasi-steady state with the load path, according toembodiments of the disclosure.

It is noted that the drawings of the disclosure are not to scale. Thedrawings are intended to depict only typical aspects of the disclosure,and therefore should not be considered as limiting the scope of thedisclosure. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As an initial matter, in order to clearly describe the currentdisclosure, it will become necessary to select certain terminology whenreferring to and describing relevant machine components within a gasturbine (GT) system. When doing this, if possible, common industryterminology will be used and employed in a manner consistent with itsaccepted meaning. Unless otherwise stated, such terminology should begiven a broad interpretation consistent with the context of the presentapplication and the scope of the appended claims. Those of ordinaryskill in the art will appreciate that often a particular component maybe referred to using several different or overlapping terms. What may bedescribed herein as being a single part may include and be referenced inanother context as consisting of multiple components. Alternatively,what may be described herein as including multiple components may bereferred to elsewhere as a single part.

In addition, several descriptive terms may be used regularly herein, andit should prove helpful to define these terms at the onset of thissection. These terms and their definitions, unless stated otherwise, areas follows. As used herein, “downstream” and “upstream” are terms thatindicate a direction relative to the flow of a fluid, such as thecombustion gas stream in a combustion section or, for example, the flowof air through the compressor. The term “downstream” corresponds to thedirection of flow of the fluid, and the term “upstream” refers to thedirection opposite to the flow. The terms “forward” and “aft,” withoutany further specificity, refer to directions, with “forward” referringto the front or compressor end of the engine, and “aft” referring to therearward or turbine end of the engine. It is often required to describeparts that are at differing radial positions with regard to a centeraxis. The term “radial” refers to movement or position perpendicular toan axis. In cases such as this, if a first component resides closer tothe axis than a second component, it will be stated herein that thefirst component is “radially inward” or “inboard” of the secondcomponent. If, on the other hand, the first component resides furtherfrom the axis than the second component, it may be stated herein thatthe first component is “radially outward” or “outboard” of the secondcomponent. The term “axial” refers to movement or position parallel toan axis. Finally, the term “circumferential” refers to movement orposition around an axis. It will be appreciated that such terms may beapplied in relation to the center axis of the turbine.

Where an element or layer is referred to as being “on,” “engaged to,”“disengaged from,” “connected to” or “coupled to” another element orlayer, it may be directly on, engaged, connected, or coupled to theother element or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly engaged to,” “directly connected to” or “directly coupledto” another element or layer, there may be no intervening elements orlayers present. Other words used to describe the relationship betweenelements should be interpreted in a like fashion (e.g., “between” versus“directly between,” “adjacent” versus “directly adjacent,” etc.). Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

As indicated above, the disclosure provides a load/unload method for agas turbine (GT) system that may allow for emissions compliance duringperiods when it normally is not provided. The disclosure also includes aGT system including a compressor feeding air to a combustion sectionthat is coupled to a turbine section. The combustion section includes aplurality of combustors with each combustor including a primarycombustion stage including a first plurality of fuel nozzles and asecondary combustion stage downstream from the primary combustion stage.The secondary combustion stage includes a second plurality of fuelnozzles. Hence, the combustion section is a two stage combustionsection. In accordance with embodiments of the disclosure, duringloading or unloading, the method progresses through each of a pluralityof progressive combustion modes that sequentially activate a differentnumber of at least one of the first and second plurality of fuelnozzles. That is, each progressive combustion mode turns on more or lessfuel nozzles to, respectively, increase or decrease the combustiontemperature and combustion flow. During loading, the method progressesthrough each of a plurality of progressive combustion modes thatsequentially activate a higher number of at least one of the first andsecond plurality of fuel nozzles. Similarly, during unloading, themethod progresses through each of a plurality of progressive combustionmodes that sequentially activate a lower number of at least one of thefirst and second plurality of fuel nozzles. In contrast to currentload/unload methods that control a temperature at an exit of thecombustor, during each combustion mode, a primary combustion stage exittemperature of a combustion gas flow (i.e., between primary andsecondary combustion stages, referred to herein as primary combustionstage exit temperature (PC SET) or mid-combustor temperature) iscontrolled to be within a predefined target range corresponding to therespective combustion mode. As a result, emissions are better controlledto remain emissions compliant.

FIG. 2 shows a cross-sectional view of an illustrative GT system 100 inwhich teachings of the disclosure may be employed. In FIG. 2, GT system100 includes an intake section 102, and a compressor 104 downstream fromintake section 102. Compressor 104 feeds air to a combustion section 106that is coupled to a turbine section 120. Compressor 104 may include oneor more stages of inlet guide vanes (IGVs) 123. As understood in theart, the angle of stages of IGVs 123 can be controlled to control an airflow volume to combustion section 106, and thus, among other things, thecombustion temperature of section 106. Combustion section 106 includes aplurality of combustors 126. Each combustor 126 includes a primarycombustion stage 108 including a first plurality of fuel nozzles, and asecondary combustion stage 110 downstream from primary combustion stage108. Secondary combustion stage 110 includes a second plurality of fuelnozzles, different than the first plurality of fuel nozzles. Exhaustfrom turbine section 120 exits via an exhaust section 122. Turbinesection 120 through a common shaft or rotor connection drives compressor104 and a load 124. Load 124 may be any one of an electrical generatorand a mechanical drive application and may be located forward of intakesection 102 (as shown) or aft of exhaust section 122. Examples of suchmechanical drive applications include a compressor for use in oil fieldsand/or a compressor for use in refrigeration. When used in oil fields,the application may be a gas reinjection service. When used inrefrigeration, the application may be in liquid natural gas (LNG)plants. Yet another load 124 may be a propeller as may be found inturbojet engines, turbofan engines and turboprop engines.

Referring to FIGS. 2 and 3, combustion section 106 may include acircular array of a plurality of circumferentially spaced combustors126. FIG. 3 shows a cross-sectional side view of combustor 126. Afuel/air mixture is burned in each combustor 126 to produce the hotenergetic combustion gas flow, which flows through a transition piece128 (FIG. 3) to turbine nozzles 130 (FIG. 3) of turbine section 120. Forpurposes of the present description, only one combustor 126 isillustrated, it being appreciated that all of the other combustors 126arranged about combustion section 106 are substantially identical to theillustrated combustor 126. Although FIG. 2 shows a plurality ofcircumferentially spaced combustors 126 and FIG. 3 shows a crosssectional side view of a combustor 126 that have come to be known in theart as can combustor systems, it is contemplated that the presentdisclosure may be used in conjunction with other combustor systemsincluding and not limited to annular combustor systems.

Referring now to FIG. 3, there is shown generally a combustor 126 for GTsystem 100 (FIG. 2) including primary combustion stage 108 and secondarycombustion stage 110. A transition piece 128 flows hot combustion gasflow to turbine nozzles 130 and the turbine blades (not shown). Primarycombustion stage 108 may include a casing 132, an end cover 134, a firstplurality of premixing fuel nozzles 140 (hereinafter simply “fuelnozzles 140”), a cap assembly 142, a flow sleeve 144, and a combustionliner 146 within flow sleeve 144. An ignition device (not shown) isprovided and preferably comprises an electrically energized spark plug.Combustion in primary combustion section 108 occurs within combustionliner 146. Combustion air is directed within combustion liner 146 viaflow sleeve 144 and may enter combustion liner 146 through a pluralityof openings formed in cap assembly 142. The air enters combustion liner146 under a pressure differential and mixes with fuel from start-up fuelnozzles (not shown) and/or first plurality of fuel nozzles 140 withincombustion liner 146. Consequently, a combustion reaction occurs withincombustion liner 146 releasing heat for the purpose of driving turbinesection 120 (FIG. 2). High-pressure air for primary combustion stage 108may enter flow sleeve 144 and a transition piece impingement sleeve 148,from an annular plenum 150. Compressor 104 (FIG. 2), which isrepresented by a series of vanes and blades at 152 and a diffuser 154 inFIG. 3, supplies this high-pressure air.

Each of first plurality of fuel nozzles 140 in primary combustion stage108 can take a variety of forms. In the example of FIG. 3, each fuelnozzle 140 may include a swirler 156, consisting of a plurality of swirlvanes that impart rotation to the entering air and a plurality of fuelspokes 158 that distribute fuel in the rotating air stream. The fuel andair then mix in an annular passage within fuel nozzle 140 beforereacting within primary reaction zone 160. However, other forms of(premixing) fuel nozzles 140 may be employed.

As shown in FIG. 3, secondary combustion stage 110 includes a secondplurality of fuel nozzles 162 for transversely injecting a secondaryfuel mixture into a combustion gas flow product of primary combustionstage 108. Fuel nozzles 162 may include any variety and number ofinjection elements for injecting the second fuel mixture. Fuel nozzles162 may extend radially into the combustion gas flow path. In oneexample, four circumferentially spaced fuel nozzles 162 are employed.However, any number may be possible.

With further regard to first plurality of fuel nozzles 140 in FIG. 3,fuel nozzles 140 may also have a variety of layouts, e.g., relative tocap assembly 142. FIGS. 4 and 5 are plan views of alternate embodimentsof a combustor cap assembly 142, as viewed from an aft end of combustionsection 106 looking in an upstream direction. Cap assembly 142illustrated in FIG. 3 corresponds to that shown in more detail in FIG.4, although it should be understood that cap assembly 142 illustrated inFIG. 5 is equally well-suited for combustion section 106 shown in FIG.3.

In FIG. 4, a center fuel nozzle 170, which is disposed about acenterline 172 of combustion section 106, is secured within a respectiveopening (not separately labeled) in a cap plate 174. A plurality (inthis example, five) outer fuel nozzles 176 are disposed about centerfuel nozzle 170 and likewise are secured within respective openings incap plate 174. Each outer fuel nozzle 176 has a centerline 172. Eachfuel nozzle 170, 176 is a bundled tube fuel nozzle having a plurality ofparallel, non-concentric mixing tubes 178 that extend through a commonfuel plenum. Cap plate 174 may include a plurality of cooling holes tofacilitate cooling of the cap face, and/or cap assembly 142 may includea second plate upstream of cap plate 174 to direct cooling flow againstthe upstream surface of cap plate 174.

In FIG. 5, a center fuel nozzle 180 is surrounded by a plurality (inthis case, five) outer fuel nozzles 182. Each outer fuel nozzle 182 hasa truncated wedge shape, such that outer fuel nozzles 182 may bepositioned in close proximity to center fuel nozzle 180 and cover amajority of the head end area. The truncated wedge shape may be definedas having a pair of radial sides 184 that extend in opposite directionsand that are joined by a first (radially inner) arcuate side 186 and asecond (radially outer) arcuate side 188. Radially outer sides 188define a radially outer perimeter of fuel nozzles 182 and, collectively,of cap assembly 142. Each fuel nozzle 182 has a respective centerline172 radially outward of centerline 172 of center fuel nozzle 180 andcombustion section 106. In this illustrative configuration, each fuelnozzle 180, 182 may have its own respective nozzle face 189 in a shapecorresponding to the shape of outer fuel nozzle 182 (wedge) or 180(round). Alternatively, tubes 178 that are part of each respective fuelnozzle 180, 182 may extend through a common cap plate (not shown). Inthis configuration, outer fuel nozzles 182 have respective fuel plenumsdefining a wedge shape, and center fuel nozzle 180 has a fuel plenumdefining a round shape. The upstream ends of mixing tubes 178 of eachfuel nozzle 180, 182 extend through a respective fuel plenum for eachfuel nozzle 180, 182. It should be noted that the specific size,spacing, and number of mixing tubes 178 shown in the Figures (includingFIGS. 4 and 5) is intended to be representative of the present bundledtube fuel nozzles 170, 176, 180, 182 and should not be construed aslimiting the present bundled tube fuel nozzles as having tubes of anyparticular size, spacing, or number. Moreover, it should be notconstrued as limiting the present bundled tube fuel nozzles as havingtubes with a single tube diameter.

In FIGS. 4 and 5, fuel nozzles 170, 176, 180, 182 are each denoted withan alphanumerical “PM” indicator, e.g., PM1, PM2 or PM3. As will bedescribed elsewhere herein, these indicators are used to indicate whichfuel nozzles are activated or operational, i.e., burning fuel, during aparticular ‘combustion mode.’ While primary combustion stage 108 isshown as including six fuel nozzles 170, 176, 180, 182 (FIGS. 4-5), andsecondary combustion stage 110 is shown as including four fuel nozzles162 (FIG. 3), it is emphasized that the teachings of the disclosure arenot limited to stages with any particular number of fuel nozzles.Further, while certain types of fuel nozzles 140, 162 have beendescribed herein, it is emphasized that a wide variety of fuel deliveryelements can be employed.

As understood in the art, a plurality of sensors 196 detect variousoperating conditions of GT system 100, and/or the ambient environmentduring operation of the system. In many instances, multiple redundantcontrol sensors may measure the same operating condition. For example,groups of redundant temperature control sensors 196 may monitor ambienttemperature, compressor discharge temperature, turbomachine exhaust gastemperature, and/or other operating temperatures of combustion gas flow(not shown) through GT system 100. Similarly, groups of other redundantpressure control sensors 196 may monitor ambient pressure, static anddynamic pressure levels at compressor 104, GT system 100 exhaust, and/orother parameters in GT system 100. Control sensors 196 may include,without limitation, flow sensors, pressure sensors, speed sensors, flamedetector sensors, valve position sensors, guide vane angle sensors,and/or any other device that may be used to sense various operatingparameters during operation of GT system 100.

It is further recognized that while some parameters are measured, i.e.,are sensed and are directly known, other parameters are calculated by amodel and are thus estimated and indirectly known. Some parameters mayalso be initially input by a user 210 (FIG. 6) to GT control system 194.In terms of the modeled parameters and applicable to the presentdisclosure, a primary combustion stage exit temperature (PCSET) of acombustion gas flow 108 (i.e., located conceptually between primarycombustion stage 108 and secondary combustion stage 110 at location 198in FIG. 3) may be calculated using a model of GT system 100. Similarly,a combustor exit temperature, i.e., conceptually at the end oftransition piece 128 at location 199 in FIG. 3, may be calculated usinga model of GT system 100. Historically, measured cycle parametersincluding but not limited to compressor pressure ratio (CPR), compressordischarge temperature (TCD), exhaust temperature (Tx), and GT outputpower have been used as modeling inputs to predict combustion exittemperatures from combustion section 106. In accordance with embodimentsof the disclosure, PCSET of a combustion gas flow will be controlledwithin a combustion mode(s) during loading and/or unloading of GT system100 to control emissions.

A load/unload control system 192 regulates an amount of fuel flow from afuel supply(ies) (not shown) to combustion section 106, and inparticular, to each of fuel nozzles 140 (FIG. 3) (170, 176, 180, 182(FIGS. 4-5), hereinafter simply “fuel nozzles 140” for brevity) and/orfuel nozzles 162 (FIG. 3) by controlling fuel valves 190. Each fuelvalve 190 is not limited to a single type of valve and may include avariety of types including but not limited to fuel control valves andfuel stop valves. Load/unload control system 192 can also control anamount of fuel split between primary combustion stage fuel nozzles 140and secondary combustion stage fuel nozzles 162, and an amount mixedwith air flowing into combustion section 106. Load/unload control system192 may also control a split of fuel between combustion stages 108 and110. Although not always applicable, load/unload control system 192 mayalso select a type of fuel for use in combustion section 106.Load/unload control system 192 may be a separate unit or may be acomponent of an overall GT control system 194 (FIG. 6), e.g., as part ofGT controller 196 (FIG. 6). Load/unload control system 192 can implementa method according to embodiments of the disclosure, as will bedescribed further herein.

FIG. 6 shows an illustrative environment demonstrating load/unloadcontrol system 192 coupled with GT system 100 (FIG. 1) via at least onecomputing device 200. Load/unload control system 192 may be a computersystem (computing device 200, FIG. 6) that includes at least oneprocessor (processing component 202, FIG. 6) and at least one memorydevice (storage component 214, FIG. 6) that executes operations tocontrol the operation of GT system 100 based at least partially onmodels, sensor inputs, calculations and/or on instructions from humanoperators. Load/unload control system 192 may include, for example, amodel of GT system 100. Operations executed by load/unload controlsystem 192 may include sensing or modeling operating parameters,modeling operational boundaries, applying operational boundary models,or applying scheduling algorithms that control operation of GT system100, such as by regulating a fuel flow to combustion section 106.Load/unload control system 192 compares operating parameters of GTsystem 100 to operational boundary models, or scheduling algorithms usedby load/unload control system 192 to generate control outputs, such as,without limitation, control instructions for valves 190 controllingactivation of fuel nozzles 140 (FIG. 3) and/or fuel nozzles 162 (FIG. 3)based on PCSET of a combustion gas flow of primary combustion stage 108.For example, the model may accept measured parameters as inputs such ascompressor air discharge temperature (TCD), fuel flow(s), exhausttemperature (Tx), GT system output power, etc., and calculate PCSET ofthe combustion gas flow after primary combustion stage 108 along withother parameters used in the control such as but not limited to: firingtemperature (Tfire) and combustor exit temperature (at location 199(FIG. 3)). Commands generated by load/unload control system 192 maycause valve(s) 190 on GT system 100 to selectively regulate fuel flow,fuel splits, and/or a type of fuel channeled between the fuelsupply(ies) and combustors 106. Other commands may be generated to causeactuators to adjust a relative position of stages of IGVs 123 (FIG. 2)or activate other control settings on GT system 100.

FIG. 7 shows a flow diagram illustrating a load/unload method for GTsystem 100, which can be performed by a computing device such asload/unload control system 192. More specifically, the FIG. 7 exampleshows a loading setting such as a start up of GT system 100. FIG. 8shows an emission compliant start up (loading) load path graph plottingexhaust temperature (Tx) versus load from FSNL (0% load) up to 50%,according to embodiments of the disclosure. FIG. 8 also includes aschematic rendition of a carbon monoxide (CO) amount in the GT exhaustin a quasi-steady state with the load path.

With reference to FIGS. 2 and 6-8, a load/unload method can be performed(e.g., executed) using at least one computing device 200, implemented asa computer program product (e.g., a non-transitory computer programproduct) for load/unload control system 192. Generally, the processincludes progressing through each of a plurality of progressivecombustion modes that sequentially activate a different number of atleast one of the first or second plurality of fuel nozzles, whilecontrolling PCSET of a combustion gas flow to be constant or within apredefined target range corresponding to the respective combustion mode.For example, for loading, the process includes progressing through eachof a plurality of progressive combustion modes that sequentiallyactivate a higher number of at least one of the first or secondplurality of fuel nozzles, while controlling a PCSET of a combustion gasflow of the primary combustion stage 108 to be within a predefinedtarget range corresponding to the respective combustion mode. As usedherein, a “combustion mode” is a state in which a certain number of fuelnozzles in primary combustion stage 108, or primary combustion stage 108and secondary combustion stage 110 are activated or operational, i.e.,they are burning fuel. Each combustion mode may also include a number ofother operational parameter settings for GT system 100 such as but notlimited to: IGV stage 123 (FIG. 2) positioning to control air flow tocombustion system 106.

As shown in FIG. 7, in process P1, an initial start up process may beperformed. The initial start up may include processing according toembodiments of the disclosure in which PC SET of a combustion gas flowis maintained within a predefined target range corresponding to therespective combustion mode, or process P1 can be conventional, i.e.,with no PCSET control. For example, a start up may begin with the rotorbeing rotated by a motor at a speed to prevent bowing of the rotor(i.e., turning gear speed) and then increasing to a speed that allowscompressor 102 (FIG. 2) to begin flowing air to combustion section 106(i.e., purge speed). The speed may then be reduced at which point fuelflow is initiated to combustion section 106, i.e., load/unload controlsystem 192 initiates fuel flow via valve(s) 190, and fuel combustionbegins. At this point, GT system 100 may go through a number of‘combustion modes’ in which a typically increasing number of fuelnozzles 170, 176, 180, 182 (FIGS. 4-5) of primary combustion stage 108are activated. In the example shown, combustion modes 1, 2 and 3 areimplemented apart from the teachings of the disclosure. For example,with reference to FIG. 4 or 5: a combustion mode 1 may activate fuelnozzle denoted PM1; a combustion mode 2 may activate fuel nozzlesdenoted PM2; and a combustion mode 3 may activate fuel nozzles denotedPM1 and PM2 (center and 2 outer) in primary combustion stage 108. Nosecondary combustion stage fuel nozzles 162 are activated in secondarycombustion stage 110 at this time. It is emphasized that process P1, asdescribed, is only illustrative and any now known or later developedinitial start up process can be employed prior to implementing theteachings of the disclosure.

In process P2, each of a plurality of progressive combustion modes thatsequentially activate a different number of at least one of the first orsecond plurality of fuel nozzles are progressed through, while alsocontrolling PCSET to be within a predefined target range correspondingto the respective combustion mode. For loading, as shown in FIG. 8, eachof the plurality of progressive combustion modes sequentially activate ahigher number of at least one of the first or second plurality of fuelnozzles. Throughout process P2, fuel flow and load output of GT system100 are increasing.

FIG. 8 shows a load path 230 (darker, solid line) according toembodiments of the disclosure that illustrates the progressivecombustion modes and controlling PCSET of a combustion gas flow. As willbe described, some of the progressive combustion modes may have adifferent predefined target range for PCSET, e.g., a predefined targetrange for PCSET for combustion mode M6 is higher than combustion mode 5,and predefined target range for PC SET for combustion mode 5 is higherthan combustion mode 4. However, a predefined target range for othercombustion modes, e.g., modes 6, 6A2 and 6A, as will be described, maybe the same. Certain combustion modes may have a larger or smallerpredefined target range than other combustion modes. It will beappreciated that the predefined target range for PCSET for eachcombustion mode is influenced by a number of factors such as but notlimited to: GT system size, location/environment; governmentregulations; fuel used; or other settings. Consequently, exactstatements of value for each predefined target range may vary widely.“Predefined” as applied to the predefined target range simply indicatesthat load/unload control system 192 calculates the acceptable rangeprior to implementation thereof, e.g., based on the above noted factorsand the particular combustion mode. FIG. 8 also shows conventional loadpath 232 (shown in dashed line) for comparison purposes. In FIG. 8, anillustrative next combustion mode upon which teachings of the disclosuremay be applied, i.e., after process P1, may be combustion mode 4. It isnoted that another combustion mode could also be the point in which theteachings of the disclosure are applied, e.g., combustion mode 3 or 5.

In process P2A, load/unload control system 192 can determine whether toprogress to a next combustion mode in a number of ways. In oneembodiment, progressing to a next successive combustion mode of theplurality of combustion modes occurs in response to one of thefollowing: in process P2A1, a compressor pressure ratio of compressor104 exceeds a respective threshold for a current combustion mode; or, inprocess P2A2, PC SET exceeds a respective maximum threshold for thecurrent combustion mode. Here, each combustion mode may have apre-assigned compressor pressure ratio (CPR) threshold, and a maximum PCSET threshold. When either threshold is exceeded, i.e., directlyexceeded or within an unacceptable range, load/unload control system 192activates more fuel nozzles to move GT system 100 along load path 230 tothe next combustion mode, if more combustion modes exist. At processP2B, load/unload control system 192 determines whether any additionalcombustion modes exist. If there are additional combustion modes, i.e.,Yes at process P2B, processing proceeds to process P2C. If not, i.e., Noat process P2B, processing proceeds to process P3, described elsewhereherein. In the current pass, additional combustion modes exist, andprocessing proceeds to process P2C.

At process P2C in FIG. 7, load/unload control system 192 may implement anext combustion mode (e.g., combustion mode 4) by activating fuelnozzles denoted PM1 and PM3 (center and 3 outer)(FIG. 4-5) in primarycombustion stage 108. Line 242 in FIG. 8 reflects a constant PCSET valueas well as the combustion mode 4 PCSET control target. The shaded bandshows a predefined target range of PCSET that is emissions compliant forcombustion mode 4, and in which PCSET may vary. As noted, an amountPCSET may vary will depend on a number of factors such as but notlimited to: GT system size, location/environment; governmentregulations; fuel used; or other settings. PCSET may be maintainedduring combustion mode 4, at process P2C in FIG. 7, by load/unloadcontrol system 192 in any now known or later developed fashion. Forexample, load/unload control system 192 may control at least one of: afuel flow rate (e.g., via valves 190) of each fuel nozzle activatedduring a respective combustion mode; or a position of at least one stageof IGVs 123 (FIG. 2) that control an air flow volume to combustionsection 106 from compressor 104. In the example shown in FIG. 8, theposition of stages of IGVs 123 is used to regulate PCSET for operationin combustion mode 4. Maintaining PCSET within a predefined target rangesuitable for combustion mode 4 results in better emissions controlduring the loading process shown, see fairly consistent, quasi-steadystate CO emissions in FIG. 8.

Subsequently, processing returns to process P2A (after process P2C),where load/unload control system 192 again determines whether toprogress to a next combustion mode. For example, in response to one ofthe following: in process P2A1, a compressor pressure ratio ofcompressor 104 exceeding a respective threshold for a current combustionmode; or, in process P2A2, a PCSET may exceed a respective maximumthreshold for the current combustion mode. If one of the thresholds isexceeded, processing progresses to process P2B. At process P2B,load/unload control system 192 determines whether any additionalcombustion modes exist. If there are additional combustion modes, i.e.,Yes at process P2B, processing proceeds to process P2C. If not, i.e., Noat process P2B, processing proceeds to process P3, described elsewhereherein.

Returning to FIG. 8, point 234 indicates when combustion mode 5 isimplemented at process P2C of FIG. 7 by load/unload control system 192.Load/unload control system 192 may activate more fuel nozzles in primarycombustion stage 108 such as fuel nozzles denoted PM2 and PM3 (4 outer)(FIGS. 4 and 5) to implement combustion mode 5. Additionally, PCSETtarget used by load/unload control system 192 is updated to anappropriate level for combustion mode 5. In the example shown in FIG. 8,the PCSET predefined target range, and thus exhaust temperature Tx,increases to a higher level, shown by line 244. The shaded band shows arange of PCSET that is emissions compliant for combustion mode 5, and inwhich PCSET may vary based on the afore-described factors. PCSET may bemaintained during combustion mode 5, at process P2C in FIG. 7, byload/unload control system 192 in any now known or later developedfashion, e.g., by controlling at least one of: a fuel flow rate of eachfuel nozzle activated during a respective combustion mode, or a positionof at least one stage of IGVs 123 (FIG. 2) that control an air flowvolume to combustion section 106 from compressor 104. In the exampleshown in FIG. 8, the position of the IGVs 123 may be used to regulatePCSET for operation in combustion mode 5. Maintaining PCSET within apredefined target range suitable for combustion mode 5 results in betteremissions control during the loading process shown, as illustrated bythe quasi-steady state CO emissions line.

Returning to FIG. 7, in process P2A (after process P2C), load/unloadcontrol system 192 can determine whether to progress to a nextcombustion mode, assuming one exists (process P2B).

Returning to FIG. 8, point 236 indicates when combustion mode 6 isimplemented at process P2C of FIG. 7 by load/unload control system 192.Load/unload control system 192 may again activate more fuel nozzles inprimary combustion stage 108 such as fuel nozzles denoted PM1, PM2 andPM3 (FIGS. 4-5) (all primary stage fuel nozzles) to implement combustionmode 6. Additionally, PCSET target used by load/unload control system192 is updated to an appropriate level for combustion mode 6. In theexample shown in FIG. 8, PCSET target, and thus exhaust temperature Tx,increase to a higher level. Line 246 reflects a constant PCSET value aswell as the combustion mode 6 PCSET control target. The shaded bandshows a predefined target range for combustion mode 6 in which PCSET mayvary. Again, PCSET may be maintained during combustion mode 6, atprocess P2C in FIG. 7, by load/unload control system 192, e.g., bycontrolling at least one of: a fuel flow rate of each fuel nozzleactivated during a respective combustion mode; and a position of atleast one stage of IGVs 123 (FIG. 2) that control an air flow volume tocombustion section 106 from compressor 104. In the example shown in FIG.8, the position of stage(s) of IGVs 123 is used to regulate PCSET foroperation in mode 6. Maintaining PCSET within a predefined target rangesuitable for combustion mode 6 results in better emissions controlduring the loading process shown.

The above-identified process can repeat as before with the notableexception now that once combustion mode 6 (all fuel nozzles in primarycombustion stage 108 are active), load/unload control system 192 maystart to activate fuel nozzles 162 in secondary combustion stage 110.For example, a seventh combustion mode, referred to as 6A2 in FIG. 8,may have load/unload control system 192 activate fuel nozzles denotedPM1, PM2 and PM3 (FIGS. 4-5) in primary combustion stage 108 (allprimary stage fuel nozzles) and also at least one of the secondplurality of fuel nozzles 162 (FIG. 3) of secondary combustion stage110. In one example, half of fuel nozzles 162 may be activated, e.g., 2of 4. The transition may occur, after process P2A (FIG. 7), i.e., inresponse to load/unload control system 192 determining whether toprogress to a next combustion mode, assuming one exists. The transitionpoint is indicated with numeral 238 in FIG. 8. Again, PCSET may bemaintained during combustion mode 6A2, at process P2C in FIG. 7, byload/unload control system 192—see line 248. During any combustion modein which all of the first plurality of fuel nozzles 140 (FIG. 3) ofprimary combustion stage 108 and the at least one of the secondplurality of fuel nozzles 162 (FIG. 3) of secondary combustion stage 110are active, load/unload control system 192 may also modify a split offuel flow between the primary and secondary combustion stages 108, 110to decrease a fuel flow to fuel nozzles 140 (FIG. 3) of primarycombustion stage 108 and increase the fuel flow to fuel nozzle(s) 162(FIG. 3) of secondary combustion stage 110. This modification on thesplit of fuel flow may be used to maintain PCSET of the combustion gasflow of primary combustion stage 108 substantially constant, i.e.,within a predefined target range. That is, the fuel split, rather thanIGV position as in previous combustion modes, may be used to regulatePCSET. This allows the position of the IGVs 123 to be used for othercontrol applications, in this example maintaining a constant,sub-isotherm, exhaust temperature. While no shading is shown, it isunderstood, some form of a predefined target range is acceptable forcombustion modes 6A2 (and subsequent mode 6A). Again, maintaining PCSETwithin a predefined target range suitable for combustion mode 6A2results in better emissions control during the loading process shown.

An eighth and final combustion mode, referred to as 6A in FIG. 8, mayhave load/unload control system 192 activate fuel nozzles denoted PM1,PM2 and PM3 (FIGS. 4-5) in primary combustion stage 108 (all primarycombustion stage fuel nozzles) and also all of fuel nozzles 162 ofsecondary combustion stage 110. The transition may occur, after processP2A (FIG. 7), i.e., in response to load/unload control system 192determining whether to progress to a next combustion mode. Thetransition point is indicated with numeral 240 in FIG. 8. Again, PCSETmay be maintained during combustion mode 6A, at process P2C in FIG. 7,by load/unload control system 192—see line 249. In the example shown inFIG. 8, fuel split between primary and secondary combustion stages 108,110 may be used to regulate PCSET. Simultaneously, the position ofstage(s) of IGVs 123 are used to keep the exhaust temperature at orbelow the maximum limit.

As illustrated by FIG. 7 and FIG. 8, for loading by load/unload controlsystem 192, each successive combustion mode of the plurality ofprogressive combustion modes initially activates a higher number of justfirst plurality of fuel nozzles 170, 176, 180, 182 (FIGS. 4-5) of theprimary combustion stage 108 than a preceding combustion mode. This isthe case for combustion modes 1-6, as described, which provide a firstset of progressive combustion modes. Subsequently, each successivecombustion mode of the plurality of progressive combustion modes maythen activate all of the first plurality of fuel nozzles 140 (FIG. 3) ofprimary combustion stage 108 and more of the second plurality of fuelnozzles 162 (FIG. 3) of secondary combustion stage 110 than a precedingcombustion mode. This is the case for combustion modes 6A2 and 6A, asdescribed, which create a second set of progressive combustion modesthat follow the first set of progressive combustion modes.

It is emphasized that the combustion modes described herein are onlyillustrative and that other sequences of combustion modes than describedmay be employed. For example, successive combustion modes can activatemore than one additional fuel nozzle. Furthermore, the first set ofprogressive combustion modes may use any combination of at least twosuccessive combustion modes selected from: a first mode in which a firstnumber of fuel nozzles of the first plurality of fuel nozzles of theprimary combustion stage is activated; a second mode in which a secondnumber of the first plurality of fuel nozzles of the primary combustionstage are activated (second number higher than the first number); athird mode in which a third number of the first plurality of fuelnozzles of the primary combustion stage are activated (third numberhigher than the first and second numbers); a fourth mode in which afourth number of the first plurality of fuel nozzles of the primarycombustion stage are activated (fourth number higher than the first,second and third numbers); a fifth mode in which a fifth number of thefirst plurality of fuel nozzles of the primary combustion stage areactivated (fifth number higher than the first, second, third and fourthnumbers); and a sixth mode in which a full number of the first pluralityof fuel nozzles of the primary combustion stage are activated (fullnumber is higher than the first, second, third, fourth and fifthnumbers). As noted, during the first set of progressive combustionmodes, the second plurality of fuel nozzles 162 of the secondarycombustion stage 110 are inactive. As noted, the second set ofprogressive combustion modes may include a seventh mode in which all ofthe first plurality of fuel nozzles of the primary combustion stage areactivated and a partial number of the second plurality of fuel nozzlesof the secondary combustion stage are activated (partial number is lessthan all of the second plurality of fuel nozzles of the secondarycombustion stage); and an eighth mode in which all of the firstplurality of fuel nozzles of the primary combustion stage are activatedand all of the second plurality fuel nozzles of the secondary combustionstage are activated. In an alternative embodiment, at least onesecondary combustion stage 110 fuel nozzle 162 may be activated prior toall of primary combustion zone 108 fuel nozzles 140 being fullyactivated.

Returning to FIGS. 7 and 8, in process P3, load/unload control system192 (or GT controller 196) (FIG. 6) may proceed with applying furtherload to GT system 100 in a conventional fashion. At process P3, as loadincreases and stages of IGVs 123 open, exhaust temperature Tx willnaturally begin to decrease from the isotherm limit. Throughout thisremainder of unit loading, i.e., until base load operation is attained,limits that govern the trajectory of the load path may include but arenot limited to combustor exit temperature limits (at location 199, FIG.3), exhaust temperature (Tx) targets, firing temperature targets, limitson temperature rise across combustion section 106, and/or baseloadcontrol settings.

The above-described process is also applicable in an unloading processfor GT system 100. In this case, as load/unload control system 192progresses through each of a plurality of progressive combustion modes,it sequentially activates a lower number of at least one of the first orsecond plurality of fuel nozzles. FIG. 9 shows an emission compliantunload path graph plotting exhaust temperature (Tx) versus load downfrom 50%, and with a schematic rendition of a carbon monoxide (CO)amount in the GT exhaust in a quasi-steady state with the load path,according to embodiments of the disclosure. FIG. 9 is generally theinverse of FIG. 8. During unloading, load/unload control system 192progresses through the plurality of progressive combustion modesincluding: a first set of progressive combustion modes in which all ofthe first plurality of fuel nozzles 140 (FIG. 3) of primary combustionstage 108 are activated and in which each successive combustion modeactivates a lower number of second plurality of fuel nozzles 162 (FIG.3) of secondary combustion stage 110 than a preceding combustion mode ofthe first set of progressive combustion modes. Further, load/unloadcontrol system 192 implements a second set of progressive combustionmodes, following the first set of progressive combustion modes, duringwhich all of second plurality of fuel nozzles 162 (FIG. 3) of thesecondary combustion stage 110 are de-activated and each successivecombustion mode activates a lower number of first plurality of fuelnozzles 140 (FIG. 3) of primary combustion stage 108 than a precedingcombustion mode of the second set of progressive combustion modes.During each combustion mode, as shown in FIG. 9, PCSET may be maintainedby load/unload control system 192 in any now known or later developedfashion. For example, load/unload control system 192 may control atleast one of: a fuel flow rate of each fuel nozzle activated during arespective combustion mode; a fuel split between stages 108, 110; or aposition of at least one stage of IGVs 123 (FIG. 2) that control an airflow volume to combustion section 106 from compressor 104. Similar toFIG. 8, each combustion mode has a PCSET that is maintained byload/unload control system 192. In one embodiment, progressing to a nextsuccessive combustion mode of the plurality of combustion modes occursin response to one of the following: a compressor pressure ratio ofcompressor 104 receding below a respective threshold for a currentcombustion mode. Here, each combustion mode may have a pre-assignedcompressor pressure ratio (Pcd) threshold. When the compressor pressureratio recedes below the threshold, load/unload control system 192activates less fuel nozzles to move GT system 100 along load path 250shown in FIG. 9 to the next combustion mode, if more combustion modesexist. In an alternative embodiment, certain combustion mode(s) maytemporarily activate more fuel nozzles during the unloading.

As described herein and shown in FIG. 6, GT control system 194(including load/unload control system 192) can include any conventionalcontrol system components used in controlling a GT system 100. Forexample, GT control system 194 can include electrical and/orelectro-mechanical components for actuating one or more components inthe GT system 100. Control system 194 can include conventionalcomputerized sub-components such as a processor, memory, input/output,bus, etc. GT control system 194 can be configured (e.g., programmed) toperform functions based upon operating conditions from an externalsource (e.g., at least one computing device 200), and/or may includepre-programmed (encoded) instructions based upon parameters of GT system100.

As noted herein, GT control system 194 can also include at least onecomputing device 200 connected (e.g., hard-wired and/or wirelessly) withGT controller 196, load/unload control system 192, and other parts of GTsystem 100 such as valves 190. In various embodiments, computing device200 is operably connected with valves 190 and other parts of GT system100, e.g., via a plurality of conventional sensors such as flow meters,temperature sensors, etc., as described herein. Computing device 200 canbe communicatively connected with GT controller 196, e.g., viaconventional hard-wired and/or wireless means. GT control system 194 isconfigured to monitor GT system 100 during operation according tovarious embodiments.

Further, computing device 200 is shown in communication with a user 210.A user 210 may be, for example, a programmer or operator. Interactionsbetween these components and computing device 200 are discussedelsewhere in this application.

As noted herein, one or more of the processes described herein can beperformed, e.g., by at least one computing device, such as computingdevice 200, as described herein. In other cases, one or more of theseprocesses can be performed according to a computer-implemented method.In still other embodiments, one or more of these processes can beperformed by executing computer program code (e.g., load/unload controlsystem 192) on at least one computing device (e.g., computing device200), causing the at least one computing device to perform a process,e.g., progressing through combustion modes according to approachesdescribed herein.

In further detail, computing device 200 is shown including a processingcomponent 212 (e.g., one or more processors), a storage component 214(e.g., a storage hierarchy), an input/output (I/O) component 216 (e.g.,one or more I/O interfaces and/or devices), and a communications pathway218. In one embodiment, processing component 212 executes program code,such as load/unload control system 192, which is at least partiallyembodied in storage component 214. While executing program code,processing component 212 can process data, which can result in readingand/or writing the data to/from storage component 214 and/or I/Ocomponent 216 for further processing. Pathway 218 provides acommunications link between each of the components in computing device200. I/O component 216 can comprise one or more human I/O devices orstorage devices, which enable user 210 to interact with computing device200 and/or one or more communications devices to enable user 210 and/orother GT component(s) 208 to communicate with computing device 214 usingany type of communications link. To this extent, GT control system 194can manage a set of interfaces (e.g., graphical user interface(s),application program interface, and/or the like) that enable human and/orsystem interaction with control system 194.

In any event, computing device 200 can comprise one or more generalpurpose computing articles of manufacture (e.g., computing devices)capable of executing program code installed thereon. As used herein, itis understood that “program code” means any collection of instructions,in any language, code or notation, that cause a computing device havingan information processing capability to perform a particular functioneither directly or after any combination of the following: (a)conversion to another language, code or notation; (b) reproduction in adifferent material form; and/or (c) decompression. To this extent, GTcontrol system 194 (and load/unload control system 192) can be embodiedas any combination of system software and/or application software. Inany event, the technical effect of computing device 200 is to progressthrough combustion modes during a load/unload of GT system 100 accordingto various embodiments herein.

Further, GT control system 194 (and load/unload control system 192) canbe implemented using a set of modules 220. In this case, a module 220can enable computing device 200 to perform a set of tasks used by GTcontrol system 194, and can be separately developed and/or implementedapart from other portions of GT control system 194. GT control system194 may include modules 220 which comprise a specific use formachine/hardware and/or software. Regardless, it is understood that twoor more modules, and/or systems may share some/all of their respectivehardware and/or software. Further, it is understood that some of thefunctionality discussed herein may not be implemented or additionalfunctionality may be included as part of computing device 200.

When computing device 200 comprises multiple computing devices, eachcomputing device may have only a portion of GT control system 194(and/or load/unload control system 192) embodied thereon (e.g., one ormore modules 220). However, it is understood that computing device 200and GT control system 194 are only representative of various possibleequivalent computer systems that may perform a process described herein.To this extent, in other embodiments, the functionality provided bycomputing device 200 and GT control system 194 can be at least partiallyimplemented by one or more computing devices that include anycombination of general and/or specific purpose hardware with or withoutprogram code. In each embodiment, the hardware and program code, ifincluded, can be created using standard engineering and programmingtechniques, respectively.

Regardless, when computing device 200 includes multiple computingdevices, the computing devices can communicate over any type ofcommunications link. Further, while performing a process describedherein, computing device 200 can communicate with one or more othercomputer systems using any type of communications link. In either case,the communications link can comprise any combination of various types ofwired and/or wireless links; comprise any combination of one or moretypes of networks; and/or utilize any combination of various types oftransmission techniques and protocols.

As discussed herein, GT control system 194 (and load/unload controlsystem 192) enables computing device 200 to control and/or monitorcombustion section 106. GT control system 194 may include logic forperforming one or more actions described herein. In one embodiment, GTcontrol system 194 may include logic to perform the above-statedfunctions. Structurally, the logic may take any of a variety of formssuch as a field programmable gate array (FPGA), a microprocessor, adigital signal processor, an application specific integrated circuit(ASIC) or any other specific use machine structure capable of carryingout the functions described herein. Logic may take any of a variety offorms, such as software and/or hardware. However, for illustrativepurposes, GT control system 194 (and load/unload control system 192) andlogic included therein will be described herein as a specific usemachine. As will be understood from the description, while logic isillustrated as including each of the above-stated functions, not all ofthe functions are necessary according to the teachings of the inventionas recited in the appended claims.

In various embodiments, GT control system 194 may be configured tomonitor operating parameters of combustion section 106, i.e., eachcombustor 106 therein, as described herein. Additionally, GT controlsystem 194 is configured to control combustion section 106, according tovarious functions described herein.

It is understood that in the flow diagram shown and described herein,other processes may be performed while not being shown, and the order ofprocesses can be rearranged according to various embodiments.Additionally, intermediate processes may be performed between one ormore described processes. The flow of processes shown and describedherein is not to be construed as limiting of the various embodiments.

The technical effect of the various embodiments of the disclosure,including, e.g., the GT control system 194 and load/unload controlsystem 192, is to run a load/unload method for GT system 100, asdescribed herein. The teachings of the disclosure can be applied to anyGT system 100 with two combustion stages to significantly drop emissionsat low load. During loading, for example, teachings of the disclosureminimize CO emissions during startup to achieve emissions compliancedown to FSNL.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof “Optional” or “optionally” means thatthe subsequently described event or circumstance may or may not occur,and that the description includes instances where the event occurs andinstances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” “approximately” and “substantially,” are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged, such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.“Approximately” as applied to a particular value of a range applies toboth values, and unless otherwise dependent on the precision of theinstrument measuring the value, may indicate +/−10% of the statedvalue(s).

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A gas turbine (GT) system, comprising: acompressor; a combustion section including a plurality of combustors, atleast one of the plurality of combustors including a primary combustionstage, the primary combustion stage including a first plurality of fuelnozzles, and a secondary combustion stage downstream from the primarycombustion stage, the secondary combustion stage including a secondplurality of fuel nozzles, the at least one of the plurality ofcombustors having a primary combustion stage exit temperature of acombustion flow between the primary combustion stage and the secondarycombustion stage; a turbine section downstream of the combustionsection; a control system coupled to the combustion section andconfigured for, during operating the gas turbine (GT) system:progressing through each of a plurality of progressive combustion modes,each of the plurality of progressive combustion modes defining arespective predefined target range for the primary combustion stage exittemperature of the combustion gas flow; wherein the plurality ofprogressive combustion modes includes at least a fifth mode, a sixthmode, and a seventh mode; wherein only a portion of the first pluralityof fuel nozzles is activated in the fifth mode and none of the secondplurality of fuel nozzles are activated in the fifth mode; wherein allof the first plurality of fuel nozzles are activated in the sixth modeand none of the second plurality of fuel nozzles are activated in thesixth mode, and wherein all of the first plurality of fuel nozzles areactivated in the seventh mode and only a portion of the second pluralityof fuel nozzles are activated in the seventh mode; and controlling theprimary combustion stage exit temperature of the combustion gas flow tobe within the respective predefined target range corresponding to therespective combustion mode during the progressing through each of theplurality of progressive combustion modes; and wherein the progressingfurther includes: unloading the gas turbine (GT) system by sequentiallyprogressing from at least the seventh mode to the sixth mode to thefifth mode, and loading the gas turbine (GT) system by sequentiallyprogressing from at least the fifth mode to the sixth mode to theseventh mode, and wherein during the loading while progressing to theseventh mode from the sixth mode, modifying a split of fuel flow betweenthe primary combustion stage and the secondary combustion stage bydecreasing a fuel flow to the first plurality of fuel nozzles andincreasing a fuel flow to the second plurality of fuel nozzles, therebymaintaining the primary combustion stage exit temperature of thecombustion gas flow within the respective predefined target range of theseventh mode.
 2. The gas turbine (GT) system of claim 1, wherein theprogressing further includes: during the loading of the gas turbine (GT)system, further sequentially progressing from the seventh mode to aneighth mode of the plurality of progressive combustion modes, whereinall of the first plurality of fuel nozzles are activated in the eighthmode and all of the second plurality of fuel nozzles are activated inthe eighth mode; and during the unloading of the gas turbine (GT)system, further sequentially progressing from the fifth mode to a fourthmode of the plurality of progressive combustion modes, wherein in thefourth mode a lower number of the first plurality of fuel nozzles areactivated than in the fifth mode and none of the second plurality offuel nozzles are activated.
 3. The gas turbine (GT) system of claim 1,wherein the controlling the primary combustion stage exit temperature ofthe combustion gas flow to be within the respective predefined targetrange during the progressing through each of the plurality ofprogressive combustion modes further includes controlling: a position ofat least one stage of inlet guide vanes that control an air flow volumeto the combustion section from the compressor.
 4. The gas turbine (GT)system of claim 1, wherein the sequential progressing from the fifthmode to the sixth mode during the loading of the gas turbine (GT) systemis in response to: a compressor pressure ratio of the compressorexceeding a threshold.
 5. The gas turbine (GT) system of claim 1,wherein the plurality of progressive combustion modes includes: a firstset of progressive combustion modes including a fourth mode, the fifthmode and the sixth mode, wherein in the fourth mode a number of thefirst plurality of fuel nozzles activated is lower than in the fifthmode; and a second set of progressive combustion modes including theseventh mode and an eighth mode.
 6. The gas turbine (GT) system of claim5, wherein the first set of progressive combustion modes furtherincludes a first mode, a second mode, and a third mode; the first modein which a first number of fuel nozzles of the first plurality of fuelnozzles of the primary combustion stage are activated; the second modein which a second number of the first plurality of fuel nozzles of theprimary combustion stage are activated, wherein the second number ishigher than the first number; the third mode in which a third number ofthe first plurality of fuel nozzles of the primary combustion stage areactivated, wherein the third number is higher than each of the first andsecond numbers; the fourth mode in which a fourth number of the firstplurality of fuel nozzles of the primary combustion stage are activated,wherein the fourth number is higher than each of the first, second andthird numbers; wherein during the first set of progressive combustionmodes, the second plurality of fuel nozzles of the secondary combustionstage are inactive.
 7. The gas turbine (GT) system of claim 6, whereinthe eighth mode in which all of the first plurality of fuel nozzles ofthe primary combustion stage are activated and all of the secondplurality fuel nozzles of the secondary combustion stage are activated.8. A non-transitory computer readable storage medium including code fora control system of a gas turbine (GT) system, the code configured tocontrol a combustion section including a plurality of combustors for aof the gas turbine (GT) system, at least one of the plurality ofcombustors including a primary combustion stage, the primary combustionstage including a first plurality of fuel nozzles, and a secondarycombustion stage downstream from the primary combustion stage, thesecondary combustion stage including a second plurality of fuel nozzles,the at least one of the plurality of combustors having a primarycombustion stage exit temperature of a combustion gas flow between theprimary combustion stage and the secondary combustion stage, the codeperforming the following during operating of the gas turbine (GT)system: progressing through each of a plurality of progressivecombustion modes, each of the plurality of progressive combustion modesdefining a respective predefined target range for the primary combustionstage exit temperature of the combustion gas flow; wherein the pluralityof progressive combustion modes includes at least a fifth mode, a sixthmode, and a seventh mode; wherein only a portion of the first pluralityof fuel nozzles is activated in the fifth mode and none of the secondplurality of fuel nozzles are activated in the fifth mode; wherein allof the first plurality of fuel nozzles are activated in the sixth modeand none of the second plurality of fuel nozzles are activated in thesixth mode, and wherein all of the first plurality of fuel nozzles areactivated and only a portion of the second plurality of fuel nozzles isactivated in the seventh mode; and controlling the primary combustionstage exit temperature of the combustion gas flow to be within therespective predefined target range corresponding to the respectivecombustion mode during the progressing through each of the plurality ofprogressive combustion modes; and wherein the progressing furtherincludes: unloading the gas turbine (GT) system by sequentiallyprogressing from at least the seventh mode to the sixth mode to thefifth mode, and loading the gas turbine (GT) system by sequentiallyprogressing from at least the fifth mode to the sixth mode to theseventh mode, and wherein during the loading while progressing to theseventh mode from the sixth mode, modifying a split of fuel flow betweenthe primary combustion stage and the secondary combustion stage bydecreasing a fuel flow to the first plurality of fuel nozzles andincreasing a fuel flow to the second plurality of fuel nozzles, therebymaintaining the primary combustion stage exit temperature of thecombustion gas flow within the respective predefined target range of theseventh mode.
 9. The non-transitory computer readable storage mediumincluding code of claim 8, wherein the progressing further includes:during the loading of the gas turbine (GT) system, further sequentiallyprogressing from the seventh mode to an eighth mode of the plurality ofprogressive combustion modes, wherein all of the first plurality of fuelnozzles are activated in the eighth mode and all of the second pluralityof fuel nozzles are activated in the eighth mode; and during theunloading of the gas turbine (GT) system, further sequentiallyprogressing from the fifth mode to a fourth mode of the plurality ofprogressive combustion modes, wherein in the fourth mode a lower numberof the first plurality of fuel nozzles are activated than in the fifthmode and none of the second plurality of fuel nozzles are activated inthe fifth mode.
 10. The non-transitory computer readable storage mediumincluding code of claim 8, wherein the controlling the primarycombustion stage exit temperature of the combustion gas flow to bewithin the respective predefined target range during the progressingthrough each of the plurality of progressive combustion modes furtherincludes controlling: a position of at least one stage of inlet guidevanes that control an air flow volume to the combustion section from acompressor of the gas turbine (GT) system.
 11. The non-transitorycomputer readable storage medium including code of claim 8, wherein thesequential progressing from the fifth mode to the sixth mode during theloading of the gas turbine (GT) system is in response to a compressorpressure ratio of the compressor exceeding a threshold.
 12. Thenon-transitory computer readable storage medium including code of claim8, wherein, the plurality of progressive combustion modes includes: afirst set of progressive combustion modes including a fourth mode, thefifth mode and the sixth mode, wherein in the fourth mode a number ofthe first plurality of fuel nozzles activated is lower than in the fifthmode; and a second set of progressive combustion modes including theseventh mode and an eighth mode.
 13. The non-transitory computerreadable storage medium including code of claim 12, wherein the firstset of progressive combustion modes further includes a first mode, asecond mode, and a third mode; the first mode in which a first number offuel nozzles of the first plurality of fuel nozzles of the primarycombustion stage are activated; the second mode in which a second numberof the first plurality of fuel nozzles of the primary combustion stageare activated, wherein the second number is higher than the firstnumber; the third mode in which a third number of the first plurality offuel nozzles of the primary combustion stage are activated, wherein thethird number is higher than each of the first and second numbers; thefourth mode in which a fourth number of the first plurality of fuelnozzles of the primary combustion stage are activated, wherein thefourth number is higher than each of the first, second and thirdnumbers; wherein during the first set of progressive combustion modes,the second plurality of fuel nozzles of the secondary combustion stageare inactive.
 14. The non-transitory computer readable storage mediumincluding code of claim 13, wherein the eighth mode in which all of thefirst plurality of fuel nozzles of the primary combustion stage areactivated and all of the second plurality fuel nozzles of the secondarycombustion stage are activated.